LED series array PWM dimness


I have a 20 LED array that I have arranged with calculations from this website: http://led.linear1.org/led.wiz . There are 10 parallel rows of 2 LEDs each in series with a 270 ohm resistor, running through 12VDC. My aim is to control the brightness of this LED array with one of the PWM pins on the Arduino, using a ULN2803 Darlington Array.

The problem is, when I use PWM and the Darlington, the LEDs are barely lit, even when sending a value of 255 to the PWM output. When I bypass the Darlington and connect the LEDs straight to ground, they glow blindingly bright. I would think that a maximum PWM value would be the same as having no PWM at all, but perhaps this is not the case?

How can I get my array of LEDs to smoothly fade from maximum brightness to dimness?

all help is greatly appreciated, thanks.


You must have your wiring wrong as there is nothing you describe that is wrong.

you sir, are absolutely correct...